Low density oriented polymer composition with inert inorganic filler

ABSTRACT

An article of manufacture comprising a polymer composition, having 30 wt % or more and 95 wt % or less inert inorganic filler, that is oriented by the steps of conditioning the polymer composition to a drawing temperature of at least 15° C. and approximately 40° C. below a softening temperature of the polymer composition; and drawing the polymer composition though a drawing die at a drawing rate of at least 0.25 m/min and with a nominal draw ratio of 1.25 or more and 8 or less to produce the article of manufacture made of the oriented polymer composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/113,265,filed May 1, 2008, which claims the benefit of U.S. ProvisionalApplication No. 60/930,145, filed on May 14, 2007, both of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to solid state drawing processes andoriented polymer compositions produced by solid state drawing processes.

2. Description of Related Art

Oriented polymer compositions are desirable for having higher strengthand stiffness over non-oriented polymer compositions. Historically,polymeric films and fibers have enjoyed the benefits of orientationthrough drawing processes. However, when a polymer cross section becomeslarger than that of a film or fiber, drawing to a controlled andconsistent shape becomes more complex and new drawing processes arenecessary.

Great Britain (GB) patent 1311885 discloses a solid state die drawingprocess to address the challenges of orienting larger cross sectionpolymer compositions, which the patent identifies as compositions havinga cross-sectional area of 0.01 square inches (6.45 square millimeters)or more or with all cross sectional dimensions greater than 0.05 inches(1.27 millimeters). The solid state die drawing process requires drawinga polymer composition billet through a lubricated drawing die in thepolymer composition's solid phase at a temperature below the polymercomposition's melting temperature (Tm). The drawing die forces thepolymer composition to converge towards a specific shape, causingalignment of polymer chains. According to GB1311885, one of thechallenges with large cross section billets is bringing the entire crosssection to a uniform temperature prior to drawing in order to allowcontrol of the extrusion velocity of the billet into the drawing die.Small cross section articles such as films and fibers do not presentsuch a challenge.

Orientation of filled polymer compositions is of particular interest.Filler offers numerous benefits, perhaps the most recognized isreduction in raw material cost for the polymer composition. Use of woodfiber fillers in oriented polymer compositions has been of particularinterest for fabricating oriented polymer compositions that serve as analternative to wood decking materials (that is, composite decking).

Organic fillers, however, are subject to handicaps including colorbleaching when exposed to the sun, and to decomposition, mold and mildewwhen exposed to humidity even within a polymer composition. Inorganicfillers are attractive because they are not subject to these handicaps.However, inorganic fillers tend to have a higher density than organicfillers. Additionally, reactive inorganic fillers such as Portlandcement and gypsum are reactive with water (see, for example, PCTpublication WO 2004/009334), which can result in an unstable polymercomposition density in humid environments.

Incorporating void volume in a filled oriented polymer compositionreduces the composition's density. U.S. Pat. No. 5,474,722 (722)discloses use of blowing agents with organic and mica fillers (seeExamples 3 and 9 in '722) in order to reduce the density of an orientedpolymer composition. Blowing agents expand to foam the polymercomposition in order to establish void volume. Foamed compositionscontain blowing agent. Foaming requires a foaming step and control offoaming agent in the process.

Cavitation is a desirable alternative for reducing an oriented polymercomposition density without the use of a blowing agent. Cavitationinduces void volume proximate to filler particles while drawing apolymer composition containing the filler particles. For example,European Patent 1242220B1 provides an example a polypropylenecomposition filled with wood filler (composition density of about onegram per cubic centimeter (cm³) that is drawn at a drawing rate of 48inches (122 centimeters) per minute to obtain an oriented polymercomposition having a density of 0.59 g/cm³ centimeter. Drawingcompositions containing up to 22 weight-percent of mica filler inpolypropylene also reveal void volumes from cavitation of up to 28.5%and densities down to 0.76 g/cm³. (W. R. Newson and F. R. Maine,ORIENTED POLYPROPYLENE COMPOSITIONS MADE WITH MICA, handout from 8thInternational Conference on Woodfiber-Plastic Composites, Madison, Wis.,May 23-25, 2005).

PCT publication WO 2004/009334 ('334) discloses cavitation duringorientation of polymer filled with reactive inorganic fillers such asPortland cement. '334 discloses both die drawn and free draw processes.The lowest density '334 reveals for a die drawn oriented polymercomposition is 0.82 g/cm³. Lower densities are reported for free drawncompositions by using a linear draw ratio of greater than eleven.However, free drawn oriented compositions having such a large lineardraw ratio (greater than eleven) tend to suffer from a low delaminationforce. That is, they delaminate or fibrillate more easily along thedrawing direction than free drawn compositions having a lower lineardraw ratio, as well as die drawn compositions. Moreover, a free drawprocess offers little control over the dimension of a final drawnarticle as compared to die drawn processes.

Using filler in an oriented polymer composition is desirable both toreduce the cost of a polymer composition and also to promote cavitation.Both of these features are attractive for preparing oriented polymercompositions that can serve as alternatives to wood in structuralapplications such as composite decking where cost and weight are bothimportant. Desirably, oriented polymer compositions in such structuralapplications are free of handicaps associated with organic fillers,density and composition instability in the presence of humidity thatreactive inorganic fillers are subject to, high densities associatedwith inorganic filler and a low delamination force with high linear drawratios.

An oriented polymer composition containing a large amount (thirtyweight-percent or more based on polymer composition weight) of inertinorganic filler that has a density comparable to or less than wood(that is, less than 0.8 g/cm³ and strength and stiffness sufficient tomeet building codes for use in structural applications is desirable. Itis further of interest to have such an oriented polymer composition thatis essentially free or completely free of blowing agent. It is stillfurther desirable for such an oriented polymer composition to have adelamination force of at least 44.5 Newtons (ten pounds force) to resistdelamination and fibrillation during use.

Measure the density of a polymer composition according to AmericanSociety for Testing and Materials (ASTM) method D-792-00.

BRIEF SUMMARY OF THE INVENTION

Experimentation leading to the present invention surprisingly revealedthat solid state drawing a polymer composition containing thirtyweight-percent or more (based on polymer composition weight) of inertinorganic filler can result in cavitation within the polymer compositionsufficient to achieve an oriented polymer composition having a densitycomparable to or less than wood (that is, less than 0.8 grams per cubiccentimeter) and a modulus sufficient to meet building codes withoutrequiring a blowing agent or a linear draw ratio of eleven. As a result,articles of the present invention surprisingly enjoy combined benefitsof high concentrations of filler (30 wt % or more by weight of polymer),low density (less than 0.8 g/cm³), high flexural modulus (1.4gigapascals or more) and high delamination force values (44.5 Newtons(N) or more; 10 pounds force or more) typically absent from compositionshaving a linear draw ratio greater than eleven while also beingvirtually, even completely free of blowing agent.

In a first aspect, the present invention relates to an article ofmanufacture, comprising a polymer composition, having 30 wt % or moreand 95 wt % or less inert inorganic filler, that is oriented by thesteps of conditioning the polymer composition to a drawing temperatureof at least 15° C. and approximately 40° C. below a softeningtemperature of the polymer composition; and drawing the polymercomposition though a drawing die at a drawing rate of at least 0.25m/min and with a nominal draw ratio of 1.25 or more and 8 or less toproduce the article of manufacture made of the oriented polymercomposition. The article of manufacture has a density of less than 0.8g/cm³ according to ASTM method 792-00, a flexural modulus of 1.4 GPa(200,000 psi) or more according to ASTM method D-790-03, across-sectional dimension defined according to a cross section of thearticle, with the cross section having a centroid and a perimeter thatdefines a shape for the cross section, with all cross sectionaldimensions greater than 1.5 mm, a delamination force value greater than44.5 N (10 lbf), and at least 30 vol % void volume proximate to theinert inorganic filler in the oriented polymer composition.

Preferred embodiments of the first aspect include any one or combinationof more than one of the following characteristics: the inert filler canbe selected from a group consisting of talc (including any individual orcombination of materials and grades of materials commonly known as oravailable as “talc”), calcium carbonate, clay and fly ash; theorientable polymer is a polyolefin; and the oriented polymer compositionis selected from polypropylene-based polymers, polyethylene-basedpolymers, polyvinyl chloride, polyesters and polyester-based polymers;the oriented polymer composition can comprise less than or equal to 3 wt% blowing agent.

According to another embodiment, the polymer composition can include 40percent by weight or more of the inert inorganic filler. The inertinorganic filler can have a density of at least 2 g/cm³. In anotheraspect, the polymer composition can be comprised of a semi-crystallinepolymer.

DETAILED DESCRIPTION OF THE INVENTION Terms

“Solid state” refers to a polymer (or polymer composition) that is belowthe softening temperature of the polymer (or polymer composition).Hence, “solid state drawing” refers to drawing a polymer or polymercomposition that is below the softening temperature of the polymer (orpolymer composition).

“Polymer composition” comprises at least one polymer component and cancontain non-polymeric components.

“Softening temperature” (Ts) for a polymer or polymer composition havingas polymer components only one or more than one semi-crystalline polymeris the melting temperature for the polymer composition.

“Melting temperature” (Tm) for a semi-crystalline polymer is thetemperature half-way through a crystalline-to-melt phase change asdetermined by differential scanning calorimetry (DSC) upon heating acrystallized polymer at a specific heating rate. Determine Tm for asemi-crystalline polymer according to the DSC procedure in ASTM methodE794-06. Determine Tm for a combination of polymers and for a filledpolymer composition also by DSC under the same test conditions in ASTMmethod E794-06. If the combination of polymers or filled polymercomposition only contains miscible polymers and only onecrystalline-to-melt phase change is evident in the a DSC curve, then Tmfor the polymer combination or filled polymer composition is thetemperature half-way through the phase change. If multiplecrystalline-to-melt phase changes are evident in a DSC curve due to thepresence of immiscible polymers, then Tm for the polymer combination orfilled polymer composition is the Tm of the continuous phase polymer. Ifmore than one polymer is continuous and they are not miscible, then theTm for the polymer combination or filled polymer composition is thehighest Tm of the continuous phase polymers.

“Softening temperature” (Ts) for a polymer or polymer composition havingas polymer components only one or more than one amorphous polymer is theglass transition temperature for the polymer composition.

“Glass transition temperature” (Tg) for a polymer or polymer compositionis the temperature half-way through a glass transition phase change asdetermined by DSC according to the procedure in ASTM method D3418-03.Determine Tg for a combination of polymers and for a filled polymercomposition also by DSC under the same test conditions in D3418-03. Ifthe combination of polymer or filled polymer composition only containsmiscible polymers and only one glass transition phase change is evidentin the DSC curve, then Tg of the polymer combination or filled polymercomposition is the temperature half-way through the phase change. Ifmultiple glass transition phase changes are evident in a DSC curve dueto the presence of immiscible amorphous polymers, then Tg for thepolymer combination or filled polymer composition is the Tg of thecontinuous phase polymer. If more than one amorphous polymer iscontinuous and they are not miscible, then the Tg for the polymercomposition or filled polymer composition is the highest Tg of thecontinuous phase polymers.

If the polymer composition contains a combination of semi-crystallineand amorphous polymers, the softening temperature of the polymercomposition is the softening temperature of the continuous phase polymeror polymer composition.

“Drawing axis” for a die is a straight line extending in the directionthat the center of mass (centroid) of a polymer composition is moving asthe polymer composition is drawn.

“Cross sections” herein are perpendicular to the drawing axis unless thereference to the cross section indicates otherwise. A cross section hasa centroid and has a perimeter that defines a shape for the crosssection.

A “cross section dimension” is the length of a straight line connectingtwo points on a cross section's perimeter and extending through thecentroid of the cross section. For example, a cross section dimension ofa rectilinear four-sided polymer composition could be the height orwidth of the polymer composition.

An artisan understands that a polymer composition typically has avariation in temperature through its cross section (that is, along across sectional dimension of the composition) during processing.Therefore, reference to temperature of a polymer composition refers toan average of the highest and lowest temperature along a cross sectionaldimension of the polymer composition. The temperature at two differentpoints along the polymer cross sectional dimension desirably differs by10% or less, preferably 5% or less, more preferably 1% or less, mostpreferably by 0% from the average temperature of the highest and lowesttemperature along the cross sectional dimension. Measure the temperaturein degrees Celsius (° C.) along a cross sectional dimension by insertingthermocouples to different points along the cross sectional dimension.

“Drawing temperature” refers to the temperature of the polymercomposition as it begins to undergo drawing in a solid state drawingdie.

“Linear Draw Ratio” is a measure of how much a polymer compositionelongates in a drawing direction (direction the composition is drawn)during a drawing process. Determine linear draw ratio while processingby marking two points on a polymer composition spaced apart by apre-orientated composition spacing. Measure how far apart those twopoints are after drawing to get an oriented composition spacing. Theratio of final spacing to initial spacing identifies the linear drawratio.

“Nominal draw ratio” is the cross sectional surface area of a polymercomposition prior as it enters a drawing die divided by the polymercross sectional area as it exits the drawing die.

“Delamination Force” is a measure of the force needed to delaminate aportion of a polymer composition along the composition's extrusiondirection. Measure delamination force for a polymer composition by meansof a delamination test as applied to a “test sample” taken from thepolymer composition.

A “test sample” is a portion of polymer composition taken from thecenter of a polymer composition (that is, the centroid of any crosssection of the test sample corresponds to a centroid of a cross sectionof the polymer composition containing the cross section of the testsample). The test sample has a length (drawing dimension orientation) of2 centimeters (cm) to 10 cm, width (dimension perpendicular to length)in a range of 8 mm to 12 mm, and uniform thickness (dimension mutuallyperpendicular to length and width) in a range of 1.25 mm to 4 mm. Use asharp razor to slice as narrow of a notch as possible in a planecontaining the length and thickness dimensions, centered in the widthdimension and extending to a notch length that is 5 to 12 mm in thelength dimension of the sample. The two tabs on either side of the notchthat extend in the length dimension and that have equal widths oforiented polymer composition on either side of the notch.

Conduct the delamination test after conditioning the test sample to 23°C. and 50% relative humidity by pulling the tabs apart at a rate of 0.2inches per minute in the width dimension of the test sample(perpendicular to the plane of the notch). Grip each tab proximate to anend of the test sample such that the distance from the center of thegrip to the end of the notch interior to the test sample defines a notchlength. Measure the force applied to the tabs until the tabs disconnectfrom one another into distinct pieces.

The maximum force measured prior to disconnecting the tabs is the “peakforce”. Determine the Delamination Force (DF) for the test sampleaccording to the following equation:

DF=(Peak Force)(notch length)/(Test Sample Thickness)

The more force that is required to completely delaminate the tabs, thegreater the delamination force value and structural integrity for thepolymer composition.

Measure the density of a polymer composition according to AmericanSociety for Testing and Materials (ASTM) method D-792-00.

Oriented Polymer Composition

The present invention, in one aspect, is an oriented polymercomposition. An oriented polymer composition comprises polymer moleculesthat have a higher degree of molecular orientation than that of apolymer composition extruded from a mixer. Typically, an orientedpolymer composition requires a specific processing step designed for thepurpose of orienting the polymer composition (for example, solid statedrawing or ram extruding through a converging die) in order to convert apolymer composition to an oriented polymer composition. The orientedpolymer composition of the present invention comprises a continuousphase of one or more orientable polymers. Typically, 90 weight-percent(wt %) or more, more typically, 95 wt % or more of the polymers in thepolymer composition are orientable polymers. All of the polymer in thepolymer composition can be orientable. Measure wt % based on totalpolymer weight in the oriented polymer composition. All of the polymersin the oriented polymer composition can be orientable polymers.

An orientable polymer is a polymer that can undergo polymer alignment.Orientable polymers can be amorphous or semi-crystalline. Herein,“semi-crystalline” and “crystalline” polymers interchangeably refer topolymers having a melt temperature (Tm). Desirable orientable polymersare one or more than one semi-crystalline polymer, particularlypolyolefin polymers (polyolefins). Polyolefins tend to readily undergocavitation in combination with filler particles presumably becausepolyolefins are relatively non-polar and as such adhere less readily tofiller particles. Linear polymers (that is, polymers in which chainbranching occurs in less than 1 of 1,000 monomer units such as linearlow density polyethylene) are even more desirable.

Suitable orientable polymers include polymers and copolymers based onpolystyrene, polycarbonate, polypropylene, polyethylene (for example,high density, very high density and ultra high density polyethylene),polyvinyl chloride, polymethylpentane, polytetrafluoroethylene,polyamides, polyesters (for example, polyethylene terephthalate) andpolyester-based polymers, polycarbonates, polyethylene oxide,polyoxymethylene, polyvinylidine fluoride and liquid crystal polymersand combinations thereof. A first polymer is “based on” a second polymerif the first polymer comprises the second polymer. For example, a blockcopolymer is based on the polymers comprising the blocks. Particularlydesirably orientable polymers include polymers based on polyethylene,polypropylene, and polyesters. More particularly desirable orientablepolymers include linear polyethylene having a Mw from 50,000 to3,000,000 g/mol; especially from 100,000 to 1,500,000 g/mol, even from750,000 to 1,500,000 g/mol.

A preferred class of polyesters (and polyester-based polymers) is thosewhich are derivable from the reaction of at least one polyhydricalcohol, suitably a linear polyhydric alcohol, preferably a diol such aslinear C2 to C6 diol with at least one polybasic acid, suitably apolycarboxylic acid. Examples of suitable polyesters includepolyethylene 2,6-naphthalate, polyethylene 1,5-naphthalate,polytetramethylene 1,2-dihydroxybenzoate, polyethylene terephthalate,polybutylene terephthalate and copolyesters, especially of ethyleneterphthalate.

Polypropylene (PP)-based polymers (that is, polymers based on PP) areone example of desirable orientable polymers for use in the presentinvention. PP-based polymers generally have a lower density than otherorientable polyolefin polymers. Therefore, PP-based polymers facilitatelighter articles than other orientable polyolefin polymers. PP-basedpolymers also offer greater thermal stability than other orientablepolyolefin polymers. Therefore, PP-based polymers may also form orientedarticles having higher thermal stability than oriented articles of otherpolyolefin polymers.

Suitable PP-based polymers include Zeigler Natta, metallocene andpost-metallocene prolypropylenes. Suitable PP-based polymers include PPhomopolymer; PP random copolymer (with ethylene or other alpha-olefinpresent from 0.1 to 15 percent by weight of monomers); PP impactcopolymers with either PP homopolymer or PP random copolymer matrix of50 to 97 percent by weight (wt %) based on impact copolymer weight andwith ethylene propylene copolymer rubber present at 3 to 50 wt % basedon impact copolymer weight prepared in-reactor or an impact modifier orrandom copolymer rubber prepared by copolymerization of two or morealpha olefins prepared in-reactor; PP impact copolymer with either a PPhomopolymer or PP random copolymer matrix for 50 to 97 wt % of theimpact copolymer weight and with ethylene-propylene copolymer rubberpresent at 3 to 50 wt % of the impact copolymer weight added viacompounding, or other rubber (impact modifier) prepared bycopolymerization of two or more alpha olefins (such as ethylene-octene)by Zeigler-Natta, metallocene, or single-site catalysis, added viacompounding such as but not limited to a twin screw extrusion process.It is desirable to use a PP-based polymer that has a melt flow rate of0.8 to 8, preferably 2 to 4, more preferably 2 to 3. It is alsodesirable use a PP-based polymer that has 55 to 70%, preferably 55 to65% crystallinity.

PP can be ultra-violet (UV) stabilized, and desirably can also be impactmodified. Particularly desirable PP is stabilized with organicstabilizers. The PP can be free of titanium dioxide pigment to achieveUV stabilization thereby allowing use of less pigments to achieve any ofa full spectrum of colors. A combination of low molecular weight andhigh molecular weight hindered amine-type light stabilizers (HALS) aredesirable additives to impart UV stabilization to PP. Suitable examplesof commercially available stabilizers include IRGASTAB™ FS 811,IRGASTAB™ FS 812 (IRGASTAB is a trademark of Ciba Specialty ChemicalsCorporation). A particularly desirable stabilizer system contains acombination of IRGASTAB™ FS 301, TINUVINT™ 123 and CHIMASSORB™ 119.(TINUVIN and CHIMASSORB are trademarks of Ciba Specialty ChemicalsCorporation).

The oriented polymer composition further comprises an inert inorganicfiller. Inorganic materials do not suffer from all of the handicaps oforganic fillers. Organic fillers include cellulosic materials such aswood fiber, wood powder and wood flour and are susceptible even within apolymer composition to color bleaching when exposed to the sun, and todecomposition, mold and mildew when exposed to humidity. However,inorganic fillers are generally denser than organic fillers. Forexample, inert inorganic fillers for use in the present inventiontypically have a density of at least two grams per cubic centimeter.Therefore, polymer compositions comprising inorganic fillers mustcontain more void volume than a polymer composition comprising the samevolume of organic fillers in order to reach the same polymer compositiondensity. Surprisingly, sufficient cavitation can occur during diedrawing to achieve an oriented polymer composition having a density ofless than 0.8 grams per cubic centimeter even when the polymercomposition contains 30 wt % or more inorganic filler.

Inorganic fillers are either reactive or inert. Reactive fillers, suchas Portland cement and gypsum, undergo a chemical reaction in thepresence of water. Inert fillers do not undergo such a chemical reactionin the presence of water. Inert fillers are more desirable than reactivefillers in order to achieve a stable polymer composition density becausethe reactive fillers attract and react with water, causing changes inpolymer composition density. Suitable inert inorganic fillers includetalc, clay (for example, kaolin), magnesium hydroxides, aluminumhydroxides, dolomite, glass beads, silica, mica, metal fillers,feldspar, Wollastonite, glass fibers, metal fibers, boron fibers, carbonblack, nano-fillers, calcium carbonate, and fly ash. Particularlydesirable inert inorganic fillers include talc, calcium carbonate, clayand fly ash. The inorganic filler can be one or a combination of morethan one inorganic filler. More particularly, an inert inorganic fillercan be any one inert inorganic filler or any combination of more thanone inert inorganic filler.

An objective of the present invention is to achieve void volume in apolymer composition containing inert inorganic filler primarily if notexclusively through cavitation rather than by means of a foaming agent.Cavitation is a process by which void volume forms proximate to fillerparticles during a drawing process as polymer is drawn away from thefiller particle. Cavitation is a means of introducing void volume intoan oriented polymer composition without having to use a blowing agent.The oriented polymer composition of the present invention contains lessthan three wt %, preferably less than two wt %, more preferably lessthan one wt %, still more preferably less than 0.5 wt % blowing agentand can be free of blowing agent. Herein, “blowing agent” includeschemical blowing agents and decomposition products therefrom. Measure wt% blowing agent relative to total oriented polymer composition weight.

Generally, the extent of cavitation (that is, amount of void volumeintroduced due to cavitation) is directly proportional to fillerconcentration. Increasing the concentration of inorganic fillerincreases the density of a polymer composition, but also tends toincrease the amount of void volume resulting from cavitation.Particularly desirable embodiments of the present oriented polymercomposition has 30 volume-percent (vol %) or more, preferably 40 vol %or more, more preferably 50 vol % or more void volume based on totalpolymer composition volume. Most desirably, the void volume is dueprimarily if not exclusively due to cavitation. An absence of blowingagent indicates void volume is due to cavitation.

Typically, oriented polymer composition of the present inventioncontains 30 wt % or more, preferably 40 wt % or more, and morepreferably 45 wt % or more filler. Filler can be present in an amount of60 wt % or more, even 70 wt % or more. Generally, the amount of filleris 95 wt % or less in order to achieve structural integrity. Determinewt % of filler based on total oriented polymer composition weight.

The oriented polymer composition of the present invention has a densityof less than 0.8 g/cm³, preferably 0.75 g/cm³ or less, more preferably0.7 g/cm³ or less. Measure oriented polymer composition densityaccording to American Society for Testing and Materials (ASTM) method792-00. A density of less than 0.8 g/cm³ is desirable to achieve adensity similar to or less than that of wood materials, which arecommonly used in markets for which the oriented polymer composition ofthe present invention is useful. Having a density similar to or lessthan that of wood is desirable to achieve ease of handling duringshipping and use. In that regard, a lower density composition is moredesirable than a higher density composition provided that the lowerdensity composition has sufficient stiffness.

One of the surprising discoveries of the present invention is thatsufficient cavitation can occur using inert inorganic filler to achievean oriented polymer composition having a density of less than 0.8 g/cm³despite having a relatively high concentration of the high density inertinorganic filler while also having a linear draw ratio of ten or less,even eight or less, even five or less when using a die drawing process.Increasing linear draw ratio results in more highly oriented polymercompositions in the drawing dimension and greater cavitation (hence,increased void volume). However, increasing linear draw ratio alsodecreases structural integrity in an oriented article, manifest by adecrease in delamination force in the drawing dimension. Fibrillation ofthe oriented composition into strands extending in the draw direction(drawing dimension) can occur when orientation becomes extreme anddelamination force too low. The present invention provides orientedpolymer compositions that enjoy a benefit from high cavitation voidvolumes without suffering from the handicap of low delamination strengthdue to linear draw ratios of eleven or more. Filled oriented polymercompositions of the present invention have delamination force values ofgreater than 44.5 Newtons (N) (ten pounds force). The delamination foris desirably 50 N (11.2 pounds force) or greater, preferably 75 N (16.8pounds force) or greater, more preferably 100 N (22.5 pounds force) orgreater and still more preferably 150 N (33.7 pounds force) or greater.

Stiffness of a polymer composition is also important for meetingbuilding codes for certain end uses for oriented polymer compositions ofthe present invention. Measure stiffness as flexural modulus (modulus ofelasticity) in accordance to ASTM method D-790-03. The oriented polymercompositions of the present invention, in combination with having adensity of less than 0.8 g/cm³, have a flexural modulus of 1.4gigapascals (GPa) (200,000 pounds per square inch (psi)) or greater,preferably 2.1 GPa (300,000 psi) or greater, more preferably 2.8 GPa(400,000 psi) or greater. A flexural modulus of 1.4 GPa or more isdesirable to meet deck board code requirements requiring a boardstiffness sufficient that the board demonstrates less than 0.09 inchesdeflection with 100 pounds per square foot weight evenly 15 distributedover a 16 inch span. (see, for example, International CodeCouncil-Evaluation Services (ICC-ES) requirement AC174 entitled:Acceptance Criteria for Deck Board Ratings and Guardrail Systems).Increasing flexural modulus is desirable to achieve even greater boardstiffness in order to safely support further weight than the coderequires.

All cross section dimensions of the oriented polymer compositions of thepresent invention are greater than 1.5 millimeters (mm), and aretypically 3 mm or greater, more typically 5 mm or greater. Such polymercompositions have relatively large cross sectional areas whichdistinguish them from films and fibers. Drawing a polymer compositionwith relatively large cross section dimension (that is, large crosssection area) has challenges that film drawing process do not have dueto processing window differences. For instance, film drawing can occurat much lower temperatures than large cross section articles. Drawstresses necessary for drawing films are much lower than for large crosssection articles. As a result, a drawing process is more likely toexceed the break stress for larger cross section articles than forfilms.

Moreover, achieving sufficient draw stress to induce enough cavitationto achieve a density of less than 0.8 g/cm³ is more challenging as thecross section dimensions of the polymer composition increase.Nonetheless, the process of the present invention (described below)overcomes each of these challenges with polymer compositions that exceedthe dimensions of a film in order to produce the oriented polymercomposition of the present invention.

Oriented polymer compositions of the present invention desirably have alow degree of connectivity between void spaces that result fromcavitation. Connectivity provides fluid communication between voidspaces and can facilitate fluid (for example, moisture) build up withinthe composition. That, in turn, can cause an undesirable increase inoriented polymer composition density, or fluctuations in densitydepending on the humidity. Desirably, less than 75%, preferably lessthan 50%, more preferably less than 25%, even more preferably less than10% of the void volume due to cavitation is accessible by water. Mostdesirably, less than 5%, even less than 1% of the void volume isaccessible by water. Measure water accessibility by immersing a polymercomposition in water and recording its change in density with time.Water uptake into the void spaces (indicating interconnectivity) isevident by an increase in density after immersion in water. In aparticularly desirable embodiment, the same accessibility values applyafter placing the oriented polymer composition in a pressure cooker.

Oriented polymer composition of the present invention can have anyconceivable cross sectional shape including circular or non-circularellipse, oval, triangle, square, rectangle, pentagon, hexagon, keyhole,arched doorway, or any other profile useful as wood trim or as deckingcomponents (for example, railings, boards, spindles).

Solid State Drawing Process

A second aspect of the present invention is a solid state drawingprocess for producing the oriented polymer composition of the firstaspect. A solid state drawing process involves pulling (that is,drawing) a polymer composition comprising an orientable polymer withsufficient force so as to induce alignment of polymer molecules in thepolymer composition. Aligning polymer molecules (that is, polymerorientation or “orientation”) is desirable to enhance the strength andmodulus (stiffness) of a polymer composition. The drawing process canalso induce cavitation in a filled polymer composition, thereby reducingthe polymer composition's density.

The solid state drawing process of the present invention involvesdrawing a polymer composition containing an inert inorganic filler and acontinuous phase of one or more orientable polymer. The polymercomposition is the same as that described above for the oriented polymercomposition. Orientation and cavitation of the polymer compound occurswhile drawing the polymer composition in the present process.

Condition the polymer composition comprising the inert inorganic fillerand orientable polymer to a drawing temperature (Td) prior to drawing.

The drawing temperature is more than ten degrees Celsius (° C.) belowthe Ts of the polymer composition. The drawing temperature can befifteen ° C. or more, twenty ° C. or more, thirty ° C. or more, evenforty ° C. or more below the polymer composition Ts. Cavitation will notoccur to any significant extent if the drawing temperature is above theorientable polymer composition's Ts. The present process requiresdrawing at a temperature of more than ten ° C. below Ts in order toachieve sufficient cavitation to reach a final density of 0.8 gram percubic centimeter (g/cm³) for the oriented polymer composition.

Generally, the drawing temperature is forty ° C. or less below thepolymer composition's Ts. Drawing a polymer composition at a drawtemperature more than forty ° C. below its Ts requires slower draw ratesthan is economically desirable in order to avoid fracturing.

Desirably, 50 weight-percent (wt %) or more, more desirably 90 wt % ormore of the polymers in a polymer composition have a Tm. More desirably,all of the polymers in the polymer composition have a Tm.

The present process is a die drawing process. That means drawing occursthrough a solid state drawing die at the drawing temperature. A diedrawing process is in contrast to a free draw process. In a free drawprocess a polymer composition necks apart from any physical constraintdrawing offers little control over the final polymer composition sizeand shape after drawing other than by controlling the polymercomposition shape prior to drawing.

Typically, a free drawn polymer composition has a cross sectional shapeproportional to its cross sectional shape prior to drawing. The presentprocess utilizes a drawing die in order to achieve better control and toenable drawing to a different cross sectional shape in the polymercomposition after drawing as compared to prior to drawing.

The die drawing process may be either batch (for example, drawingdiscrete polymer billets) or continuous (for example, drawing acontinuous feed of polymer composition from an extruder).

A drawing die provides a physical constraint that helps to define apolymer composition's size and shape by directing polymer movementduring the drawing process. Die drawing occurs by conditioning a polymercomposition to a drawing temperature and then pulling a polymercomposition through a shaping channel in a drawing die.

The shaping channel constricts the polymer composition in at least onedimension causing the polymer composition to draw to a general crosssectional shape. Die drawing processes advantageously provide greatercontrol in shaping a polymer composition during a drawing process thanis available in a free draw process.

The present process is not limited to a specific drawing die. However,the present invention advantageously employs a substantiallyproportional drawing die. A substantially proportional drawing diedirects drawing of a polymer composition in such a manner so as toachieve an oriented polymer composition having a cross sectional shapeproportional to that of the polymer composition entering theproportional drawing die. Such a die balances polymer forces directedtowards a polymer cross section centroid such that variations in polymercomposition or processing conditions do not affect the shape of thefinal oriented polymer composition. Therefore, such a drawing dieadvantageously provides predictable control over the final polymercomposition shape despite changes in polymer composition or drawingprocess conditions.

Draw the polymer composition through a drawing die at a specific drawrate. The draw rate is instrumental in determining the density andmodulus of a resulting oriented polymer composition. Faster draw ratescan advantageously induce more cavitation (therefore, produce a lowerdensity product) generate a greater extent of orientation (highermodulus) and generally provide a more economically efficient process.Draw rate is a linear rate that polymer composition exits a drawing diein a drawing direction.

Part of the present surprising discovery is that to achieve a density ofless than 0.8 g/cm³ by means of cavitation and a modulus of 1.4 GPa(200,000 psi) the process must use a draw rate of 0.25 meter per minute(m/min) or faster. Desirably, the draw rate is 0.5 m/min or faster,preferably one m/min or faster, and more preferably two m/min or faster.An upper limit for the draw rate is limited primarily by the drawingforce necessary to achieve a specific draw rate. The drawing forceshould be less than the tensile strength of the polymer composition atthe drawing temperature in order to avoid fracturing the polymercomposition. Typically, the draw rate is 30.5 meters per minute orslower, more typically nine meters per minute or slower.

Another part of the present discovery is that sufficient cavitation toprovide a polymer composition with a density of less than 0.8 g/cm³ anda flexural modulus of 1.4 GPa or greater is possible using a linear drawratio of ten or less, even eight or less, even five or less.WO2004/009334 discloses oriented polymer compositions containingreactive inorganic fillers and their examples illustrate orientedpolymer composition having a density less than 0.8 g/cm³ only when usinga free draw process implementing a linear draw ratio of greater than 11.

A sample with such a high linear draw ratio will have an undesirably lowdelamination force (see, for example, Comparative Examples M-P below).

The present invention ideally utilizes a nominal draw ratio of 1.25 ormore and can employ a nominal draw ratio of 1.5 or more, two or more,three or more, four or more, five or more, even six or more. Highernominal draw ratios are desirable to achieve higher polymer orientation.Increasing polymer orientation increases polymer composition strengthand stiffness. However, increasing nominal draw ratio also increaseslinear draw ratio. Therefore, it is desirable to use a nominal drawratio that is 8 or less, preferably 6 or less, more preferably 5 orless, even more preferably 4 or less in order to maximize the structuralintegrity of the oriented polymer composition. The nominal draw ratiocan be 3 or less, even 2 or less.

EXAMPLES

The following examples serve to further illustrate embodiments of thepresent invention.

Preparation of Polymer Compositions

TABLE 1 Initial Polymer Compositions Polymer Com- Compo- posi- sitionT_(s) tion (° C.) Polymer Filler (a) 163 Nucleated polypropylene- 46 wt% Talc composition ethylene random based on total composition copolymerhaving 0.5 weight. Talc composition wt % ethylene component is 50-60 wt% talc and and a melt flow rate of 40-50 wt % magnesium 3 (for example.,carbonates having a median INSPIRETM D404.01, diameter of 16.4 microns.INSPIRE is a trademark (for example, TC-100 of The Dow Chemical fromLuzenac) Company) (b) 163 [same as (a)] 46 wt % Calcium carbonate havinga mean particle size of 1.1 microns, with wt % based on totalcomposition weight (for example, Supercoat from Imersys) (c) 148Polypropylene-ethylene 46 wt % fly ash as random copolymer havingreceived from Headwaters 3.2 wt % ethylene and a Resources (for example,melt flow rate of 1.9 Class F from Headwaters (for example, 6D83KResources) from The Dow Chemical Company). (d) 148 [same as (c)] [sameas (a)] (e) 160 Polypropylene [same as (a)] homopolymer with a melt flowrate of 2.8 (for example, 5D37 from The Dow Chemical Company) (f) 163[same as (a)] 50 wt % Portland Cement (g) 163 [same as (a)] 40 wt %Portland Cement

Prepare polymer compositions “a” through “g” (described in Table 1) bythe following procedure: compound the polymer and filler using asuitable mixing extruder, for example a Farrell Continuous Mixer (FCM)or co-rotating twin screw extruder. Feed polymer and filler at thespecified weight ratio through standard loss in weight feeders. Melt thepolymer in the mixing extruder and mix the filler into the polymermatrix to form a polymer/filler mix. Feed the polymer/filler mix fromthe mixing extruder into a suitable pumping device (for example, asingle screw extruder or gear pump) and then through a multi-hole stranddie to produce multiple strands of the polymer/filler mix. Cool thestrands under water and cut them into pellets.

For Compositions (a)-(e), re-extrude the pellets into a polymercomposition billet. Alternatively the polymer/filler mix may be pumpeddirectly from the pumping device through a profile die and then cooledto produce a polymer composition billet without forming pellets andre-extruding. As yet another alternative, the polymer/filler mix may bepumped directly from the pumping device, through a profile die, cooledto a drawing temperature and then drawn to an oriented polymercomposition.

For Compositions (f) and (g), injection mold the composition into a ASTMD-790 type 1 tensile bar for use in Comparative Examples (Comp Exs) M-P.

Drawing Procedure Examples (Exs) Smaller Scale Compositions

Mill a billet of polymer composition corresponding to the desiredexample to have cross section dimensions to match the nominal draw ratiofor a specific example. Table 2 provides the dimensions of the billetsfor the corresponding nominal draw ratios. Mill an initial tab on an endof each billet that is smaller in dimension than any point in theshaping channel and longer than the length of the die. The tab extendsthrough the die for attaching an actuator to pull the rest of the billetthrough the die.

TABLE 2 Milled Billet Dimensions Milled Billet Milled Billet NominalDraw Ratio Width cm (in) Height cm (in) 2 1.80 (0.707) 0.450 (0.177) 42.54 (1.0)  0.635 (0.25) 

Draw Exs 1(a)-1(f) using a proportional die with a die exit opening of1.27 cm (0.5″)×0.3175 cm (0.125″) and a rectangular shaping channelhaving cross section dimensions substantially proportional to oneanother. The walls spanning the height of the channel converge at 15°angle to reduce the width while the walls spanning the width dimensionconverge at a 3.83° angle to reduce the height. This die is describedand illustrated further in a U.S. patent application having Ser. No.60/858,122 and entitled SUBSTANTIALLY PROPORTIONAL DRAWING DIE FORPOLYMER COMPOSITIONS (see, Proportional Die description in the Examples,incorporated herein by reference). The die channel opening has a crosssection that is larger and proportional to the cross section of thebillet entering the die channel, as well as the die exit opening.

Condition each billet to a drawing temperature prior to drawing throughthe drawing die. Draw a billet through the drawing die by extending theinitial tab through the drawing die, gripping the tab with an actuatorand then pulling the billet through the drawing die using an MTShydraulic tester, model number 205. Center the billet in the shapingchannel of the die. Draw the billet slowly at first to orient theleading edge and then bring to a specific draw rate while maintainingthe die at the drawing temperature. The drawn polymer compositionrepresents the Example or Comparative Example.

Each of Comparative Examples A-I and Examples 1(a)-1(f) has arectangular cross section with a width of 9-10 mm and a height of2.1-2.6 mm and has less than 5% of the void volume in each accessible bywater in a water immersion test.

TABLE 3 Draw Temp. ° C. Draw Oriented Flex Delamination Polymer belowpolymer Rate Density Modulus Force N Ex Comp. composition Ts NDR¹ cm/minLDR² g/cm3 GPa (lb force) Comp a 10 4 2.54 5.7 1.09 4.6 NM* Ex A Comp a10 4 25.4 7.3 0.95 4.2 NM* Ex B Comp a 10 4 127 9.9 0.82 3.9 NM* Ex CComp a 10 4 254 10.1 0.84 3.7 NM* Ex D Comp a 10 4 508 9.7 0.85 3.6 NM*Ex E Comp a 20 4 2.54 7.2 0.89 4.2 49.4 (11.1) Ex F Comp a 20 4 25.4 9.70.82 4.9 54.3 (12.2) Ex G 1(a) a 20 4 50.8 10.3 0.79 5.0 51.6 (11.6)1(b) a 20 4 101 11.6 0.75 5.5 99.6 (22.4) 1(c) a 20 4 127 12.8 0.73 5.370.3 (15.8) Comp a 30 4 2.54 6.7 0.93 4.0 187 (42)  Ex H 1(d) a 30 425.4 9.7 0.75 4.5 84.5 (19)  Comp a 30 4 127 13.6 0.65 6.6   28 (6.3)³Ex I 1(e) a 30 4 254 14.4 0.68 NM* 82.7 (18.6) 1 (f) a 30 4 508 13.70.69 NM* 73.4 (16.5) *“NM” means “not measured” ¹NDR is “nominal drawratio” ²LDR is “linear draw ratio” ³It is expected that this lowdelamination value is an outlier, perhaps due to unobserved void(s) inthe center of the sample. The trend in samples 1(d)-1(e) suggests thisvalue should be between 84.5 and 82.7 Newtons. As measured, however,this delamination value is outside our claimed range and so the exampleis listed as a Comparative Example.

Comparative Examples A-H and Examples 1(a)-1(f) illustrate the effect ofdrawing temperature on oriented polymer composition density for apolymer composition similar to composition “a”. Examples 1(a)-(f) arefree of blowing agent.

Examples (Exs) 2-7 Larger Scale Compositions

Mill a billet of polymer composition corresponding to the desiredexample to have cross section dimensions to match a nominal draw ratiofor a specific example. Table 4 provides the dimensions of the billetsfor the corresponding nominal draw ratios. Mill an initial tab on an endof each billet that is smaller in dimension than any point in theshaping channel and longer than the length of the die. The tab extendsthrough the die for attaching an actuator to pull the rest of the billetthrough the die.

TABLE 4 Milled Billet Dimensions Milled Billet Milled Billet NominalDraw Ratio Width cm (in) Height cm (in) 1.8 6.81 (2.68) 3.40 (1.34) 410.16 (4.0)  5.08 (2.0) 

Condition each billet to the desired temperature prior to drawingthrough the drawing die. Draw a billet through a drawing die byextending the initial tab through the drawing die; gripping the tab withan actuator and then pulling the billet through the drawing die. Centerthe billet in the shaping channel of each die. Draw the billet slowly atfirst to orient the leading edge and then bring to a specific draw rate.Draw the billet through a proportional die.

The drawing die used is a proportional die proportional similar to thatused in Example 1. The proportional die for Examples 2-7 has a die exitopening of 5.08 cm (2″)×2.54 cm (1″) and a rectangular shaping channelhaving cross section dimensions substantially proportional to oneanother. The walls spanning the height of the channel converge at 15°angle towards a plane centrally located between them in order to reducethe width of the die channel while progressing towards the channel'sexit opening. The walls spanning the width dimension converge at a 3.83°angle towards a plane centrally located between them in order to reducethe height of the die channel while progressing towards the cannel'sexit opening. The die channel entrance opening has a cross section thatis larger and proportional to both the cross section of the billetentering the die channel and the die exit opening. At the die exit was aland with length of 1.27 cm (0.5″).

TABLE 5 Conditions and Results for Exs 2-7 Ex Polymer Draw Temp. (° C.Draw Oriented Flex Delamination Polymer below polymer Rate DensityModulus Force N Ex Comp. composition Ts) NDR (m/min) LDR (g/cm³) (GPa)(lb force) 2 a 20 2 2.4 9.5 0.65 2.8 75.2 (16.9)  3 a 15 2 2.4 8.5 0.803.0 127 (28.5) 4 a 18 4 2.4 10.5 0.78 3.3 158 (35.5) 5 a 18 2 2.4 9 0.802.8 122 (27.4) 6 e 23 2 2.4 10 0.73 2.4 89 (20)  7 e 18 2 2.4 8.5 0.803.0 110 (24.7)

Each of Exs 2-7 had a width between 29 and 36 mm and a height between 14and 18 mm. Each of Exs 2-7 has less than 5% of the void volumeaccessible by water.

Exs 2-7 illustrate large scale oriented polymer compositions of thepresent invention prepared with various polymer compositions, drawingtemperatures and linear draw ratios. Exs 2-7 are free of blowing agentand have less than 5% of their void volume accessible by water in animmersion test.

Comp. Ex. M-P: Free Drawn Sample with Portland Cement

Free draw the tensile bars of compositions (f) and (g) according to theparameters in Table 6. Mark three lines on the gauge area of the tensilebars. Space each line 2.54 centimeters (one inch) apart from itsneighboring line(s) perpendicular to the drawing direction. Draw thetensile bars in an oven after allowing the tensile bars to equilibrateto the specified drawing temperature. Grip one end of the tensile barwith a stationary (anchoring) self tightening grip. Grip an opposing endof the tensile bar with a mobile self-tightening grip. Using acaterpillar type puller draw the tensile bar by pulling the mobileself-tightening grip affixed to the tensile bar at a rate of 2.4 meters(eight feet) per minute to draw the tensile bar 0.6-0.9 meters(two-three feet).

Determine linear draw ratio by measuring the distance between markedlines on the tensile bars after drawing and dividing that by the 2.54centimeter (one inch) spacing from prior to drawing. The linear drawratio is the average ratio determined for the two line spacings.

Measure density, flexural modulus and delamination force in the samemanner as the other examples. Note, because these comparative examplesare free drawn, there is no drawing die so the drawing processeffectively has a nominal draw ratio of one.

TABLE 6 Draw Temp. Flex Delami- Poly- (° C. below Mod- nation Comp. merpolymer com- Density ulus Force N Ex Comp. position Ts) LDR (g/cm3)(GPa) (lb force) M f 5 9 0.68 21.4 (4.8) N f 5 9 0.74 20.9 (4.7) O f 108.5 0.66 36.9 (8.3) p g 10 7.25 0.78 24.0 (5.4)

Comparative Examples M-P illustrate that free drawn samples containing40-50 wt % Portland cement suffer from a Delamination Force that is lessthan 44.5 Newtons (10 pounds force). Attempts at free drawingcomparative examples of these polymer compositions at LDR values greaterthan 9 were unsuccessful because the tensile bars would break.

Based on data presently being collected and compiled, it is expectedthat increasing the linear draw ratio on a filled polymer compositionwill reduce the Delamination Force of the resulting oriented polymercomposition. Furthermore, it is expected that increasing the amount ofPortland cement to levels above 50 wt % (for example, 60 wt %) of thepolymer composition will retain or reduce the Delamination Forcerelative to compositions with 40-50 wt % Portland cement that are freedrawn at the same drawing temperature and LDR.

1. An article of manufacture, comprising: a polymer composition, having30 wt % or more and 95 wt % or less inert inorganic filler, that isoriented by the steps of conditioning the polymer composition to adrawing temperature of at least 15° C. and approximately 40° C. below asoftening temperature of the polymer composition; and drawing thepolymer composition though a drawing die at a drawing rate of at least0.25 m/min and with a nominal draw ratio of 1.25 or more and 8 or lessto produce the article of manufacture made of the oriented polymercomposition, the article of manufacture having: (a) a density of lessthan 0.8 g/cm³ according to ASTM method 792-00; (b) a flexural modulusof 1.4 GPa (200,000 psi) or more according to ASTM method D-790-03; (c)a cross-sectional dimension defined according to a cross section of thearticle, with the cross section having a centroid and a perimeter thatdefines a shape for the cross section, with all cross sectionaldimensions greater than 1.5 mm; (d) a delamination force value greaterthan 44.5 N (10 lbf); and (e) at least 30 vol % void volume proximate tothe inert inorganic filler in the oriented polymer composition.
 2. Thearticle of claim 1, wherein the inert inorganic filler is selected froma group consisting of talc, calcium carbonate, clay and fly ash.
 3. Thearticle of claim 1, wherein the oriented polymer composition iscomprised of at least one polymer selected from the group consisting ofpolypropylene-based polymers, polyethylene-based polymers, polyvinylchloride, polyesters and polyester-based polymers.
 4. The article ofclaim 1, wherein the oriented polymer composition further comprises lessthan or equal to 3 weight-percent of a blowing agent.
 5. The article ofclaim 1, comprising 40 percent by weight or more of the inert inorganicfiller.
 6. The article of claim 1, wherein the polymer composition iscomprised of a semi-crystalline polymer.
 7. The article of claim 1,comprising 40 percent by weight or more of the inert inorganic filler.8. The article of claim 1, wherein the polymer composition is comprisedof a semi-crystalline polymer.
 9. The article of claim 1, wherein theinert inorganic filler has a density of at least 2 g/cm³.